Energy Cost of Vacuum Kilns

Estimates of the electricity and heating fuel consumption and cost for vacuum kiln operation. June 28, 2006

Question
I am working on a business plan that involves the installation of one or more vacuum kilns. I need a ballpark figure for the energy cost per board foot of red oak.
Also, can I estimate the life of this equipment for amortization?

Forum Responses
(Sawing and Drying Forum)
From contributor A:
I have a spreadsheet which lets me calculate a pretty wide range of items, one of which is the energy use per various qualifications. Keep in mind that every vacuum kiln is different. A discontinuous vacuum uses a different amount compared to an RF kiln compared to a Woodmizer compared to our VacDry kilns.

That said, a typical VacDry costs about $19.50 per 1000 boardfeet when drying 4/4 material such as Red Oak and paying $0.13/kW. 8/4 pushes this up to roughly $29, and 12/4 to $68 (the cost per 1M rises in line with the length of the schedule). That amount doesn't factor in any costing for a heat source, but it does include the control panel, the heating and vacuum pumps, and a standard cooling tower system.

For each of our VacDry kilns, every component is sized for the specific capacity and drying rate of that kiln. The energy costs scale practically linearly along the range of sizes we manufacture. To the best of my knowledge, our energy use versus drying rate is the lowest in the vacuum kiln industry. Therefore, your mileage may vary. My spreadsheet says it would cost $180 for a 75% efficient fuel oil boiler to dry 3500 boardfeet calculated roughly via the total water and BTU's required, at $2.33 a gallon for the fuel, so very roughly $52 per 1M. Total for this hypothetical system: $70.91 per 1M; or $19.50 per 1M with a woodwaste boiler.

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From the original questioner:
Thanks for the numbers. Do you have any information on longevity of your kilns? Or are all the installations quite new? Concerning the heat source, are the boilers steam-producing units, or just water heaters? Is it possible to use an outdoor wood furnace like the ones for heating a house?

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From contributor B:
Our oldest installation is nearing 8 years old. When I designed these kilns, the intent was to avoid all the problems I had been fixing in other companies' vacuum kilns for the previous 15 years. With a stainless steel chamber and well designed heating system, there is nothing in the kiln to wear out. IF the cooling water is kept clean, a liquid sealed vacuum pump will run for decades.

We started a new 4000 bf kiln last week. It is drying HM baseball bat billets at an Amish mill. The source of heat is a little outdoor boiler. We have also used plant steam. We are about to ship another kiln to Hawaii where burning is out and energy is expensive. Their heat will be from a little gas boiler that is rated at 92% efficiency.

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From contributor C:
Not to be picky but aren't you being a little cute comparing your electric bill and assuming a 0 cost for running the boiler with a conventional kiln burning oil? Comparing a conventional kiln burning wood for heat and a vacuum kiln burning wood for heat with both buying electricity, at the same price, might be more helpful. Or a vacuum kiln burning oil for heat and a conventional kiln burning oil for heat and buying electricity at the same rate. Apples and apples.

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The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor W:
We have three vacuum kilns currently at our operation. I have found the cost to be fairly insignificant, as we use a small wood fired. The cost for labor exceeds the cost of drying for us, as it is very labor intensive to load and unload.